1. Field of the Invention
The present invention relates to a process for producing 2-perfluoroalkylethyl alcohol, and more particularly to a process of obtaining 2-perfluoroalkylethyl alcohol by sulfation and subsequent hydrolysis using 2-perfluoroalkylethyl iodide and bis(2-perfluoroalkylethyl)sulfate.
2. Description of Related Art
2-perfluoroalkylethyl alcohol is used as an intermediate for the production of substances useful for water- and oil-repellent, surfactants, mold release agents and so on.
There is generally known, as a process for producing 2-perfluoroalkylethyl alcohol, a process of sulfonating 2-perfluoroalkylethyl iodide with fuming sulfuric acid to produce 2-perfluoroalkylethyl sulfate and hydrolyzing 2-perfluoroalkylethyl sulfate to obtain 2-perfluoroalkylethyl alcohol (refer to Japanese Examined Patent Publication (Kokoku) No. 40-19085 and Published Japanese Translation No. 5-507269 of the PCT Application).
With reference to Japanese Examined Patent Publication (Kokoku) No. 40-19085, it is understood that such a conventional production process is composed of two reactions which are sequentially executed. A first reaction is a sulfation reaction of reacting 2-perfluoroalkylethyl iodide represented by RfCH2CH2I with fuming sulfuric acid to produce 2-perfluoroalkylethyl sulfate (fluoroalkyl hydrogen sulfate), represented by RfCH2CH2OSO2OH, and I2. A second reaction is a hydrolysis reaction of hydrolyzing 2-perfluoroalkylethyl sulfate produced in the first reaction with an aqueous acid to produce 2-perfluoroalkylethyl alcohol, represented by RfCH2CH2OH, and sulfuric acid.
In the above conventional production process, bis(2-perfluoroalkylethyl)sulfate and an iodide (2-perfluoroalkylethyl iodide, the same shall apply hereinafter) are produced as by-products and a yield of 2-perfluoroalkylethyl alcohol (RfCH2CH2OH) as the target substance contained in a final reaction mixture (final mixture) which also contains the by-products is about 80% at most. A main by-product is bis(2-perfluoroalkylethyl)sulfate and an amount of the iodide in the final mixture is as small as about several % by weight which amount is determined by a gas chromatographic analysis. It is necessary to decrease an amount of the by-product contained in the final mixture, particularly bis(2-perfluoroalkylethyl)sulfate so as to attain a high yield.
Bis(2-perfluoroalkylethyl)sulfate is a by-product in the above first reaction (sulfation reaction). Although it is known that bis(2-perfluoroalkylethyl)sulfate is hydrolyzed to produce 2-perfluoroalkylethyl alcohol as the target substance (refer to Japanese Examined Patent Publication (Kokoku) No. 40-19085), more time and more severe acidic conditions than those of hydrolysis of 2-perfluoroalkylethyl sulfate, are required and therefore it is difficult to hydrolyze bis(2-perfluoroalkylethyl)sulfate to produce 2-perfluoroalkylethyl alcohol in the above second reaction. When the second reaction is carried out under severe conditions where bis(2-perfluoroalkylethyl)sulfate is also hydrolyzed, an ether represented by RfCH2CH2OCH2CH2Rf′ is produced as a by-product by a side reaction between bis(2-perfluoroalkylethyl)sulfate and 2-perfluoroalkylethyl alcohol.
Bis(2-perfluoroalkylethyl)sulfate can also be hydrolyzed under alkali conditions after being isolated (refer to Japanese Examined Patent Publication (Kokoku) No. 40-19085). In the reaction, an olefin represented by RfCH═CH2 is produced as a by-product by a desulphation reaction of bis(2-perfluoroalkylethyl)sulfate.
As described above, a method of reducing an amount of bis(2-perfluoroalkylethyl)sulfate that is produced as a by-product in the above first reaction (sulfation reaction) and contained in the final mixture, which method includes hydrolyzing bis(2-perfluoroalkylethyl)sulfate, has disadvantages associated with by-products such as ether or olefin, and the reaction time.
In the above first reaction, by using fuming sulfuric acid in a large excess amount based on 2-perfluoroalkylethyl iodide as a raw material, an amount of bis(2-perfluoroalkylethyl)sulfate produced as a by-product can also be decreased. However, considering the reactor size, the amount of fuming sulfuric acid to be used, and the amount of waste water produced by neutralization and dilution, this method is inefficient and is not suited for industrial production.
As an improvement of a conventional production process, the addition of an oxidizing agent in a hydrolysis step is proposed so as to decrease an amount of iodide contained in the final product (refer to Japanese Patent No. 3,438,905). However, the addition of the oxidizing agent in the hydrolysis step in this improved process does not always sufficiently suppress the production of the by-product iodide. Furthermore in this improved process, the production of the by-product bis(2-perfluoroalkylethyl)sulfate is not taken into consideration at all. As described above, since the amount of iodide contained in the final mixture is as small as about several % by weight even in the case of a conventional production process, the yield of 2-perfluoroalkylethyl alcohol cannot be effectively increased by this improved process.